Method and apparatus for processing high level syntax in image/video coding system

ABSTRACT

A video decoding method performed by a video decoding apparatus, according to the present document, comprises the steps of: acquiring general constraint information from a bitstream; parsing, from the bitstream, a flag indicating whether or not the general constraint information includes information about constraints to which output layer sets conform; parsing the information about the constraints in the general constraint information on the basis of the flag; and decoding a current picture on the basis of the information about the constraints, wherein the general constraint information includes number information and alignment information about the constraints, and, within the general constraint information, the alignment information may be present after the number information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/KR2021/006904, filed on Jun. 3, 2021, which claims the benefit ofU.S. Provisional Application No. 63/034,946, filed on Jun. 4, 2020, and63/033,853, filed on Jun. 3, 2020. The disclosures of the priorapplications are incorporated by reference in their entirety.

TECHNICAL FIELD

The present technology relates to a method and an apparatus forprocessing high level syntax in case of encoding/decoding image/videoinformation in an image/video coding system.

BACKGROUND

Recently, the demand for high resolution, high quality image/video suchas 4K, 8K or more Ultra High Definition (UHD) image/video is increasingin various fields. As the image/video resolution or quality becomeshigher, relatively more amount of information or bits are transmittedthan for conventional image/video data. Therefore, if image/video dataare transmitted via a medium such as an existing wired/wirelessbroadband line or stored in a legacy storage medium, costs fortransmission and storage are readily increased.

Moreover, interests and demand are growing for virtual reality (VR) andartificial reality (AR) contents, and immersive media such as hologram;and broadcasting of images/videos exhibiting image/video characteristicsdifferent from those of an actual image/video, such as gameimages/videos, are also growing.

Therefore, a highly efficient image/video compression technique isrequired to effectively compress and transmit, store, or play highresolution, high quality images/videos showing various characteristicsas described above.

SUMMARY

A technical subject of the present document is to provide a method andan apparatus for enhancing image/video coding efficiency.

Another technical subject of the present document is to provide a methodand an apparatus for efficiently processing high level syntax in case ofcoding image/video.

Still another technical subject of the present document is to provide amethod and an apparatus for skipping parsing of general constraintinformation in processing high level syntax.

Yet still another technical subject of the present document is toprovide a method and an apparatus for processing profile, tier, andlevel information separately from general constraint information inprocessing high level syntax.

According to an embodiment of the present document, a video decodingmethod performed by a video decoding apparatus may include: obtaininggeneral constraint information from a bitstream; parsing, from thebitstream, a flag representing whether information on constraints towhich output layer sets conform is present in the general constraintinformation; parsing the information on the constraints from the generalconstraint information based on the flag; and decoding a current picturebased on the information on the constraints, wherein the generalconstraint information includes number information on the constraintsand alignment information, and wherein the alignment information ispresent next to the number information in the general constraintinformation.

According to another embodiment of the present document, a videoencoding method performed by a video encoding apparatus may include:performing inter prediction or intra prediction for a current block in acurrent picture; generating prediction information for the current blockbased on the inter prediction or the intra prediction; and encodingimage information including the prediction information, wherein theimage information includes a flag representing whether information onconstraints to which output layer sets conform is present in generalconstraint information of the image information, wherein the generalconstraint information includes number information on the constraintsand alignment information, and wherein the alignment information ispresent next to the number information in the general constraintinformation.

According to still another embodiment of the present document, acomputer-readable digital storage medium including information causing avideo decoding apparatus to perform a video decoding method, wherein thevideo decoding method may include: obtaining general constraintinformation from image information; parsing, from the image information,a flag representing whether information on constraints to which outputlayer sets conform is present in the general constraint information;parsing the information on the constraints from the general constraintinformation based on the flag; and decoding a current picture based onthe information on the constraints, wherein the general constraintinformation includes number information on the constraints and alignmentinformation, and wherein the alignment information is present next tothe number information in the general constraint information.

According to an embodiment of the present document, the overallimage/video compression efficiency can be enhanced.

According to an embodiment of the present document, the generalconstraint information can be efficiently signaled in signaling theimage/video information.

According to an embodiment of the present document, the parsing of thegeneral constraint information can be skipped in processing the highlevel syntax.

According to an embodiment of the present document, the profile, tier,and level information can be processed separately from the generalconstraint information in processing the high level syntax.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an example of a video/image codingsystem to which embodiments of the present document are applicable.

FIG. 2 is a diagram schematically illustrating a configuration of avideo/image encoding apparatus to which the embodiments of the presentdocument are applicable.

FIG. 3 is a diagram schematically illustrating a configuration of avideo/image decoding apparatus to which the embodiments of the presentdocument are applicable.

FIG. 4 illustrates an example of a schematic picture decoding procedureto which an embodiment of the present document is applicable.

FIG. 5 illustrates an example of a schematic picture encoding procedureto which an embodiment of the present document is applicable.

FIG. 6 exemplarily illustrates a hierarchical structure for codedimage/video.

FIGS. 7 and 8 schematically illustrate a video/image encoding method andan example of related components according to an embodiment of thepresent document.

FIGS. 9 and 10 schematically illustrate a video/image decoding methodand an example of related components according to an embodiment of thepresent document.

FIG. 11 illustrates an example of a content streaming system to whichembodiments disclosed in the present document are applicable.

DETAILED DESCRIPTION

The disclosure of the present document may be modified in various forms,and specific embodiments thereof will be described and illustrated inthe drawings. The terms used in the present document are used to merelydescribe specific embodiments, but are not intended to limit thedisclosed method in the present document. An expression of a singularnumber includes an expression of ‘at least one’, so long as it isclearly read differently. The terms such as “include” and “have” areintended to indicate that features, numbers, steps, operations,elements, components, or combinations thereof used in the document existand it should be thus understood that the possibility of existence oraddition of one or more different features, numbers, steps, operations,elements, components, or combinations thereof is not excluded.

In addition, each configuration of the drawings described in the presentdocument is an independent illustration for explaining functions asfeatures that are different from each other, and does not mean that eachconfiguration is implemented by mutually different hardware or differentsoftware. For example, two or more of the configurations may be combinedto form one configuration, and one configuration may also be dividedinto multiple configurations. Without departing from the gist of thedisclosed method of the present document, embodiments in whichconfigurations are combined and/or separated are included in the scopeof the disclosure of the present document.

In the present document, the term “/” and “,” should be interpreted toindicate “and/or.” For instance, the expression “A/B” may mean “A and/orB.” Further, “A, B” may mean “A and/or B.” Further, “A/B/C” may mean “atleast one of A, B, and/or C.” Also, “A/B/C” may mean “at least one of A,B, and/or C.”

Further, in the document, the term “or” should be interpreted toindicate “and/or.” For instance, the expression “A or B” may comprise 1)only A, 2) only B, and/or 3) both A and B. In other words, the term “or”in the present document should be interpreted to indicate “additionallyor alternatively.”

Further, the parentheses used in the present document may mean “forexample”. Specifically, in case that “prediction (intra prediction)” isexpressed, it may be indicated that “intra prediction” is proposed as anexample of “prediction”. In other words, the term “prediction” in thepresent document is not limited to “intra prediction”, and “intraprediction” is proposed as an example of “prediction”. Further, even incase that “prediction (i.e., intra prediction)” is expressed, it may beindicated that “intra prediction” is proposed as an example of“prediction”.

In the present document, technical features individually explained inone drawing may be individually implemented or simultaneouslyimplemented.

Hereinafter, embodiments of the present document will be described indetail with reference to the accompanying drawings. In addition, likereference numerals are used to indicate like elements throughout thedrawings, and the same descriptions on the like elements may be omitted.

The present document relates to video/image coding. For example, amethod/embodiment disclosed in the present document may be applied to amethod disclosed in a versatile video coding (VVC) standard. Inaddition, the method/embodiment disclosed in the present document may beapplied to a method disclosed in an essential video coding (EVC)standard, AOMedia Video 1 (AV1) standard, 2nd generation of audio videocoding standard (AVS2), or a next-generation video/image coding standard(e.g., H.267, H.268, etc.).

Various embodiments related to video/image coding are presented in thepresent document, and the embodiments may be combined with each otherunless otherwise stated.

FIG. 1 illustrates an example of a video/image coding system to whichthe embodiments of the present document may be applied.

Referring to FIG. 1 , a video/image coding system may include a firstdevice (a source device) and a second device (a reception device). Thesource device may transmit encoded video/image information or data tothe reception device through a digital storage medium or network in theform of a file or streaming.

The source device may include a video source, an encoding apparatus, anda transmitter. The receiving device may include a receiver, a decodingapparatus, and a renderer. The encoding apparatus may be called avideo/image encoding apparatus, and the decoding apparatus may be calleda video/image decoding apparatus. The transmitter may be included in theencoding apparatus. The receiver may be included in the decodingapparatus. The renderer may include a display, and the display may beconfigured as a separate device or an external component.

The video source may acquire video/image through a process of capturing,synthesizing, or generating the video/image. The video source mayinclude a video/image capture device and/or a video/image generatingdevice. The video/image capture device may include, for example, one ormore cameras, video/image archives including previously capturedvideo/images, and the like. The video/image generating device mayinclude, for example, computers, tablets and smartphones, and may(electronically) generate video/images. For example, a virtualvideo/image may be generated through a computer or the like. In thiscase, the video/image capturing process may be replaced by a process ofgenerating related data.

The encoding apparatus may encode input video/image. The encodingapparatus may perform a series of procedures such as prediction,transform, and quantization for compaction and coding efficiency. Theencoded data (encoded video/image information) may be output in the formof a bitstream.

The transmitter may transmit the encoded image/image information or dataoutput in the form of a bitstream to the receiver of the receivingdevice through a digital storage medium or a network in the form of afile or streaming. The digital storage medium may include variousstorage mediums such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and thelike. The transmitter may include an element for generating a media filethrough a predetermined file format and may include an element fortransmission through a broadcast/communication network. The receiver mayreceive/extract the bitstream and transmit the received bitstream to thedecoding apparatus.

The decoding apparatus may decode the video/image by performing a seriesof procedures such as dequantization, inverse transform, and predictioncorresponding to the operation of the encoding apparatus.

The renderer may render the decoded video/image. The renderedvideo/image may be displayed through the display.

In the present document, a video may refer to a series of images overtime. A picture generally refers to the unit representing one image at aparticular time frame, and a slice/tile refers to the unit constitutinga part of the picture in terms of coding. A slice/tile may include oneor more coding tree units (CTUs). One picture may consist of one or moreslices/tiles. One picture may consist of one or more tile groups. Onetile group may include one or more tiles. A brick may represent arectangular region of CTU rows within a tile in a picture). A tile maybe partitioned into multiple bricks, each of which consisting of one ormore CTU rows within the tile. A tile that is not partitioned intomultiple bricks may be also referred to as a brick. A brick scan is aspecific sequential ordering of CTUs partitioning a picture in which theCTUs are ordered consecutively in CTU raster scan in a brick, brickswithin a tile are ordered consecutively in a raster scan of the bricksof the tile, and tiles in a picture are ordered consecutively in araster scan of the tiles of the picture. A tile is a rectangular regionof CTUs within a particular tile column and a particular tile row in apicture. The tile column is a rectangular region of CTUs having a heightequal to the height of the picture and a width specified by syntaxelements in the picture parameter set. The tile row is a rectangularregion of CTUs having a height specified by syntax elements in thepicture parameter set and a width equal to the width of the picture). Atile scan is a specific sequential ordering of CTUs partitioning apicture in which the CTUs are ordered consecutively in CTU raster scanin a tile whereas tiles in a picture are ordered consecutively in araster scan of the tiles of the picture. A slice includes an integernumber of bricks of a picture that may be exclusively contained in asingle NAL unit. A slice may consist of either a number of completetiles or only a consecutive sequence of complete bricks of one tile. Inthe present document, tile group and slice may be used interchangeably.For example, in the present document, a tile group/tile group header maybe referred to as a slice/slice header.

A pixel or a pel may mean a smallest unit constituting one picture (orimage). Also, ‘sample’ may be used as a term corresponding to a pixel. Asample may generally represent a pixel or a value of a pixel, and mayrepresent only a pixel/pixel value of a luma component or only apixel/pixel value of a chroma component.

A unit may represent a basic unit of image processing. The unit mayinclude at least one of a specific region of the picture and informationrelated to the region. One unit may include one luma block and twochroma (ex. Cb, cr) blocks. The unit may be used interchangeably withterms such as block or area in some cases. In a general case, an M×Nblock may include samples (or sample arrays) or a set (or array) oftransform coefficients of M columns and N rows. Alternatively, thesample may mean a pixel value in the spatial domain, and when such apixel value is transformed to the frequency domain, it may mean atransform coefficient in the frequency domain.

The unit may be interchangeably used with the term such as a block or anarea in some cases. Generally, an M×N block may represent samplescomposed of M columns and N rows or a group of transform coefficients.The sample may generally represent a pixel or a value of the pixel, andmay also represent only the pixel/pixel value of a luma component, andalso represent only the pixel/pixel value of a chroma component. Thesample may be used as the term corresponding to a pixel or a pelconfiguring one picture (or image).

FIG. 2 is a diagram schematically illustrating the configuration of avideo/image encoding apparatus to which the embodiments of the presentdocument may be applied. Hereinafter, what is referred to as the videoencoding apparatus may include an image encoding apparatus.

Referring to FIG. 2 , the encoding apparatus 200 may include and beconfigured with an image partitioner 210, a predictor 220, a residualprocessor 230, an entropy encoder 240, an adder 250, a filter 260, and amemory 270. The predictor 220 may include an inter predictor 221 and anintra predictor 222. The residual processor 230 may include atransformer 232, a quantizer 233, a dequantizer 234, and an inversetransformer 235. The residual processor 230 may further include asubtractor 231. The adder 250 may be called a reconstructor orreconstructed block generator. The image partitioner 210, the predictor220, the residual processor 230, the entropy encoder 240, the adder 250,and the filter 260, which have been described above, may be configuredby one or more hardware components (e.g., encoder chipsets orprocessors) according to an embodiment. In addition, the memory 270 mayinclude a decoded picture buffer (DPB), and may also be configured by adigital storage medium. The hardware component may further include thememory 270 as an internal/external component.

The image partitioner 210 may split an input image (or, picture, frame)input to the encoding apparatus 200 into one or more processing units.As an example, the processing unit may be called a coding unit (CU). Inthis case, the coding unit may be recursively split according to aQuad-tree binary-tree ternary-tree (QTBTTT) structure from a coding treeunit (CTU) or the largest coding unit (LCU). For example, one codingunit may be split into a plurality of coding units of a deeper depthbased on a quad-tree structure, a binary-tree structure, and/or aternary-tree structure. In this case, for example, the quad-treestructure is first applied and the binary-tree structure and/or theternary-tree structure may be later applied. Alternatively, thebinary-tree structure may also be first applied. A coding procedureaccording to the present document may be performed based on a finalcoding unit which is not split any more. In this case, based on codingefficiency according to image characteristics or the like, the maximumcoding unit may be directly used as the final coding unit, or asnecessary, the coding unit may be recursively split into coding units ofa deeper depth, such that a coding unit having an optimal size may beused as the final coding unit. Here, the coding procedure may include aprocedure such as prediction, transform, and reconstruction to bedescribed later. As another example, the processing unit may furtherinclude a prediction unit (PU) or a transform unit (TU). In this case,each of the prediction unit and the transform unit may be split orpartitioned from the aforementioned final coding unit. The predictionunit may be a unit of sample prediction, and the transform unit may be aunit for inducing a transform coefficient and/or a unit for inducing aresidual signal from the transform coefficient.

The encoding apparatus 200 may subtract the prediction signal (predictedblock, prediction sample array) output from the inter predictor 221 orthe intra predictor 222 from the input image signal (original block,original sample array) to generate a residual signal (residual block,residual sample array), and the generated residual signal is transmittedto the transformer 232. In this case, as illustrated, a unit forsubtracting the prediction signal (prediction block, prediction samplearray) from an input image signal (original block, original samplearray) in the encoder 200 may be referred to as a subtractor 231. Thepredictor 220 may perform prediction on a processing target block(hereinafter, referred to as a current block) and generate a predictedblock including prediction samples for the current block. The predictor220 may determine whether intra prediction or inter prediction isapplied in units of a current block or CU. The predictor 220 maygenerate various kinds of information on prediction, such as predictionmode information, and transmit the generated information to the entropyencoder 240, as is described below in the description of each predictionmode. The information on prediction may be encoded by the entropyencoder 240 and output in the form of a bitstream.

The intra predictor 222 may predict a current block with reference tosamples within a current picture. The referenced samples may be locatedneighboring to the current block, or may also be located away from thecurrent block according to the prediction mode. The prediction modes inthe intra prediction may include a plurality of non-directional modesand a plurality of directional modes. The non-directional mode mayinclude, for example, a DC mode or a planar mode. The directional modemay include, for example, 33 directional prediction modes or 65directional prediction modes according to the fine degree of theprediction direction. However, this is illustrative and the directionalprediction modes which are more or less than the above number may beused according to the setting. The intra predictor 222 may alsodetermine the prediction mode applied to the current block using theprediction mode applied to the neighboring block.

The inter predictor 221 may induce a predicted block of the currentblock based on a reference block (reference sample array) specified by amotion vector on a reference picture. At this time, in order to decreasethe amount of motion information transmitted in the inter predictionmode, the motion information may be predicted in units of a block, asub-block, or a sample based on the correlation of the motioninformation between the neighboring block and the current block. Themotion information may include a motion vector and a reference pictureindex. The motion information may further include inter predictiondirection (L0 prediction, L1 prediction, Bi prediction, or the like)information. In the case of the inter prediction, the neighboring blockmay include a spatial neighboring block existing within the currentpicture and a temporal neighboring block existing in the referencepicture. The reference picture including the reference block and thereference picture including the temporal neighboring block may also bethe same as each other, and may also be different from each other. Thetemporal neighboring block may be called the name such as a collocatedreference block, a collocated CU (colCU), or the like, and the referencepicture including the temporal neighboring block may also be called acollocated picture (colPic). For example, the inter predictor 221 mayconfigure a motion information candidate list based on the neighboringblocks, and generate information indicating what candidate is used toderive the motion vector and/or the reference picture index of thecurrent block. The inter prediction may be performed based on variousprediction modes, and for example, in the case of a skip mode and amerge mode, the inter predictor 221 may use the motion information ofthe neighboring block as the motion information of the current block. Inthe case of the skip mode, the residual signal may not be transmittedunlike the merge mode. A motion vector prediction (MVP) mode mayindicate the motion vector of the current block by using the motionvector of the neighboring block as a motion vector predictor, andsignaling a motion vector difference.

The predictor 220 may generate a prediction signal based on variousprediction methods to be described below. For example, the predictor 220may apply intra prediction or inter prediction for prediction of oneblock and may simultaneously apply intra prediction and interprediction. This may be called combined inter and intra prediction(CIP). In addition, the predictor may be based on an intra block copy(IBC) prediction mode or based on a palette mode for prediction of ablock. The IBC prediction mode or the palette mode may be used forimage/video coding of content such as games, for example, screen contentcoding (SCC). IBC basically performs prediction within the currentpicture, but may be performed similarly to inter prediction in that areference block is derived within the current picture. That is, IBC mayuse at least one of the inter prediction techniques described in thepresent document. The palette mode may be viewed as an example of intracoding or intra prediction. When the palette mode is applied, a samplevalue in the picture may be signaled based on information on the palettetable and the palette index.

The prediction signal generated by the predictor (including the interpredictor 221 and/or the intra predictor 222) may be used to generate areconstructed signal or may be used to generate a residual signal.

The transformer 232 may generate transform coefficients by applying atransform technique to the residual signal. For example, the transformtechnique may include at least one of a discrete cosine transform (DCT),a discrete sine transform (DST), a graph-based transform (GBT), or aconditionally non-linear transform (CNT). Here, GBT refers totransformation obtained from a graph when expressing relationshipinformation between pixels in the graph. CNT refers to transformationobtained based on a prediction signal generated using all previouslyreconstructed pixels. Also, the transformation process may be applied toa block of pixels having the same size as a square or may be applied toa block of a variable size that is not a square.

The quantizer 233 quantizes the transform coefficients and transmits thesame to the entropy encoder 240, and the entropy encoder 240 encodes thequantized signal (information on the quantized transform coefficients)and outputs the encoded signal as a bitstream. Information on thequantized transform coefficients may be referred to as residualinformation. The quantizer 233 may rearrange the quantized transformcoefficients in the block form into a one-dimensional vector form basedon a coefficient scan order and may generate information on thetransform coefficients based on the quantized transform coefficients inthe one-dimensional vector form.

The entropy encoder 240 may perform various encoding methods such as,for example, exponential Golomb, context-adaptive variable length coding(CAVLC), and context-adaptive binary arithmetic coding (CABAC). Theentropy encoder 240 may encode information necessary for video/imagereconstruction (e.g., values of syntax elements, etc.) other than thequantized transform coefficients together or separately. Encodedinformation (e.g., encoded video/image information) may be transmittedor stored in units of a network abstraction layer (NAL) unit in the formof a bitstream. The video/image information may further includeinformation on various parameter sets, such as an adaptation parameterset (APS), a picture parameter set (PPS), a sequence parameter set(SPS), or a video parameter set (VPS). Also, the video/image informationmay further include general constraint information. In the presentdocument, information and/or syntax elements transmitted/signaled fromthe encoding apparatus to the decoding apparatus may be included invideo/image information. The video/image information may be encodedthrough the encoding procedure described above and included in thebitstream. The bitstream may be transmitted through a network or may bestored in a digital storage medium. Here, the network may include abroadcasting network and/or a communication network, and the digitalstorage medium may include various storage media such as USB, SD, CD,DVD, Blu-ray, HDD, and SSD. A transmitting unit (not shown) and/or astoring unit (not shown) for transmitting or storing a signal outputfrom the entropy encoder 240 may be configured as internal/externalelements of the encoding apparatus 200, or the transmitting unit may beincluded in the entropy encoder 240.

The quantized transform coefficients output from the quantizer 233 maybe used to generate a prediction signal. For example, the residualsignal (residual block or residual samples) may be reconstructed byapplying dequantization and inverse transform to the quantized transformcoefficients through the dequantizer 234 and the inverse transform unit235. The adder 250 may add the reconstructed residual signal to theprediction signal output from the inter predictor 221 or the intrapredictor 222 to generate a reconstructed signal (reconstructed picture,reconstructed block, reconstructed sample array). When there is noresidual for the processing target block, such as when the skip mode isapplied, the predicted block may be used as a reconstructed block. Theadder 250 may be referred to as a restoration unit or a restorationblock generator. The generated reconstructed signal may be used forintra prediction of a next processing target block in the currentpicture, or may be used for inter prediction of the next picture afterbeing filtered as described below.

Meanwhile, luma mapping with chroma scaling (LMCS) may be applied duringa picture encoding and/or reconstruction process.

The filter 260 may improve subjective/objective image quality byapplying filtering to the reconstructed signal. For example, the filter260 may generate a modified reconstructed picture by applying variousfiltering methods to the reconstructed picture, and store the modifiedreconstructed picture in the memory 270, specifically, in a DPB of thememory 270. The various filtering methods may include, for example,deblocking filtering, a sample adaptive offset, an adaptive loop filter,a bilateral filter, and the like. The filter 260 may generate variouskinds of information related to the filtering, and transfer thegenerated information to the entropy encoder 240 as described later inthe description of each filtering method. The information related to thefiltering may be encoded by the entropy encoder 240 and output in theform of a bitstream.

The modified reconstructed picture transmitted to the memory 270 may beused as a reference picture in the inter predictor 221. When the interprediction is applied through the encoding apparatus, predictionmismatch between the encoding apparatus 200 and the decoding apparatusmay be avoided and encoding efficiency may be improved.

The DPB of the memory 270 may store the modified reconstructed picturefor use as the reference picture in the inter predictor 221. The memory270 may store motion information of a block from which the motioninformation in the current picture is derived (or encoded) and/or motioninformation of blocks in the picture, having already been reconstructed.The stored motion information may be transferred to the inter predictor221 to be utilized as motion information of the spatial neighboringblock or motion information of the temporal neighboring block. Thememory 270 may store reconstructed samples of reconstructed blocks inthe current picture, and may transfer the reconstructed samples to theintra predictor 222.

Meanwhile, image/video coding according to the present disclosure mayinclude multilayer-based image/video coding. The multilayer-basedimage/video coding may include scalable coding. The multilayer-basedcoding or scalable coding may process input signals for each layer.Input signals (input image/picture) may differ in at least one ofresolution, frame rate, bit-depth, color format, aspect ratio, and viewdepending on the layers. In this case, it is possible to reduce repeatedtransmission/processing of information and increase compressionefficiency by performing prediction between layers using a differencebetween layers, namely, based on scalability.

FIG. 3 is a diagram for schematically explaining the configuration of avideo/image decoding apparatus to which the embodiments of the presentdocument may be applied.

Referring to FIG. 3 , the decoding apparatus 300 may include andconfigured with an entropy decoder 310, a residual processor 320, apredictor 330, an adder 340, a filter 350, and a memory 360. Thepredictor 330 may include an inter predictor 331 and an intra predictor332. The residual processor 320 may include a dequantizer 321 and aninverse transformer 322. The entropy decoder 310, the residual processor320, the predictor 330, the adder 340, and the filter 350, which havebeen described above, may be configured by one or more hardwarecomponents (e.g., decoder chipsets or processors) according to anembodiment. Further, the memory 360 may include a decoded picture buffer(DPB), and may be configured by a digital storage medium. The hardwarecomponent may further include the memory 360 as an internal/externalcomponent.

When the bitstream including the video/image information is input, thedecoding apparatus 300 may reconstruct the image in response to aprocess in which the video/image information is processed in theencoding apparatus illustrated in FIG. 2 . For example, the decodingapparatus 300 may derive the units/blocks based on block split-relatedinformation acquired from the bitstream. The decoding apparatus 300 mayperform decoding using the processing unit applied to the encodingapparatus. Therefore, the processing unit for the decoding may be, forexample, a coding unit, and the coding unit may be split according tothe quad-tree structure, the binary-tree structure, and/or theternary-tree structure from the coding tree unit or the maximum codingunit. One or more transform units may be derived from the coding unit.In addition, the reconstructed image signal decoded and output throughthe decoding apparatus 300 may be reproduced through a reproducingapparatus.

The decoding apparatus 300 may receive a signal output from the encodingapparatus of FIG. 2 in the form of a bitstream, and the received signalmay be decoded through the entropy decoder 310. For example, the entropydecoder 310 may parse the bitstream to derive information (e.g.,video/image information) necessary for image reconstruction (or picturereconstruction). The video/image information may further includeinformation on various parameter sets such as an adaptation parameterset (APS), a picture parameter set (PPS), a sequence parameter set(SPS), or a video parameter set (VPS). In addition, the video/imageinformation may further include general constraint information. Thedecoding apparatus may further decode picture based on the informationon the parameter set and/or the general constraint information.Signaled/received information and/or syntax elements described later inthe present document may be decoded may decode the decoding procedureand obtained from the bitstream. For example, the entropy decoder 310decodes the information in the bitstream based on a coding method suchas exponential Golomb coding, context-adaptive variable length coding(CAVLC), or context-adaptive arithmetic coding (CABAC), and outputsyntax elements required for image reconstruction and quantized valuesof transform coefficients for residual. More specifically, the CABACentropy decoding method may receive a bin corresponding to each syntaxelement in the bitstream, determine a context model by using a decodingtarget syntax element information, decoding information of a decodingtarget block or information of a symbol/bin decoded in a previous stage,and perform an arithmetic decoding on the bin by predicting aprobability of occurrence of a bin according to the determined contextmodel, and generate a symbol corresponding to the value of each syntaxelement. In this case, the CABAC entropy decoding method may update thecontext model by using the information of the decoded symbol/bin for acontext model of a next symbol/bin after determining the context model.The information related to the prediction among the information decodedby the entropy decoder 310 may be provided to the predictor (interpredictor 332 and intra predictor 331), and residual values on which theentropy decoding has been performed in the entropy decoder 310, that is,the quantized transform coefficients and related parameter information,may be input to the residual processor 320.

The residual processor 320 may derive a residual signal (residual block,residual samples, or residual sample array). Also, information onfiltering among the information decoded by the entropy decoder 310 maybe provided to the filter 350. Meanwhile, a receiving unit (not shown)for receiving a signal output from the encoding apparatus may be furtherconfigured as an internal/external element of the decoding apparatus300, or the receiving unit may be a component of the entropy decoder310. Meanwhile, the decoding apparatus according to the present documentmay be called a video/image/picture decoding apparatus, and the decodingapparatus may be divided into an information decoder(video/image/picture information decoder) and a sample decoder(video/image/picture sample decoder). The information decoder mayinclude the entropy decoder 310, and the sample decoder may include atleast one of the dequantizer 321, the inverse transformer 322, the adder340, the filter 350, the memory 360, an inter predictor 332, and anintra predictor 331.

The dequantizer 321 may dequantize the quantized transform coefficientsto output the transform coefficients. The dequantizer 321 may rearrangethe quantized transform coefficients in a two-dimensional block form. Inthis case, the rearrangement may be performed based on a coefficientscan order performed by the encoding apparatus. The dequantizer 321 mayperform dequantization for the quantized transform coefficients using aquantization parameter (e.g., quantization step size information), andacquire the transform coefficients.

The inverse transformer 322 inversely transforms the transformcoefficients to acquire the residual signal (residual block, residualsample array).

In the present document, at least one of quantization/dequantizationand/or transform/inverse transform may be omitted. When thequantization/dequantization is omitted, the quantized transformcoefficient may be referred to as a transform coefficient. When thetransform/inverse transform is omitted, the transform coefficient may becalled a coefficient or a residual coefficient or may still be calledthe transform coefficient for uniformity of expression.

In the present document, the quantized transform coefficient and thetransform coefficient may be referred to as a transform coefficient anda scaled transform coefficient, respectively. In this case, the residualinformation may include information on transform coefficient(s), and theinformation on the transform coefficient(s) may be signaled throughresidual coding syntax. Transform coefficients may be derived based onthe residual information (or information on the transformcoefficient(s)), and scaled transform coefficients may be derivedthrough inverse transform (scaling) on the transform coefficients.Residual samples may be derived based on inverse transform (transform)of the scaled transform coefficients. This may be applied/expressed inother parts of the present document as well.

The predictor 330 may perform the prediction of the current block, andgenerate a predicted block including the prediction samples of thecurrent block. The predictor may determine whether the intra predictionis applied or the inter prediction is applied to the current block basedon the information on prediction output from the entropy decoder 310,and determine a specific intra/inter prediction mode.

The predictor 330 may generate a prediction signal based on variousprediction methods to be described later. For example, the predictor mayapply intra prediction or inter prediction for prediction of one block,and may simultaneously apply intra prediction and inter prediction. Thismay be called combined inter and intra prediction (CIP). In addition,the predictor may be based on an intra block copy (IBC) prediction modeor based on a palette mode for prediction of a block. The IBC predictionmode or the palette mode may be used for image/video coding of contentsuch as games, for example, screen content coding (SCC). IBC maybasically perform prediction within the current picture, but may beperformed similarly to inter prediction in that a reference block isderived within the current picture. That is, IBC may use at least one ofthe inter prediction techniques described in the present document. Thepalette mode may be considered as an example of intra coding or intraprediction. When the palette mode is applied, information on the palettetable and the palette index may be included in the video/imageinformation and signaled.

The intra predictor 331 may predict the current block by referring tothe samples in the current picture. The referred samples may be locatedin the neighborhood of the current block, or may be located apart fromthe current block according to the prediction mode. In intra prediction,prediction modes may include a plurality of non-directional modes and aplurality of directional modes. The intra predictor 331 may determinethe prediction mode to be applied to the current block by using theprediction mode applied to the neighboring block.

The inter predictor 332 may derive a predicted block for the currentblock based on a reference block (reference sample array) specified by amotion vector on a reference picture. In this case, in order to reducethe amount of motion information being transmitted in the interprediction mode, motion information may be predicted in the unit ofblocks, subblocks, or samples based on correlation of motion informationbetween the neighboring block and the current block. The motioninformation may include a motion vector and a reference picture index.The motion information may further include information on interprediction direction (L0 prediction, L1 prediction, Bi prediction, andthe like). In case of inter prediction, the neighboring block mayinclude a spatial neighboring block existing in the current picture anda temporal neighboring block existing in the reference picture. Forexample, the inter predictor 332 may construct a motion informationcandidate list based on neighboring blocks, and derive a motion vectorof the current block and/or a reference picture index based on thereceived candidate selection information. Inter prediction may beperformed based on various prediction modes, and the information on theprediction may include information indicating a mode of inter predictionfor the current block.

The adder 340 may generate a reconstructed signal (reconstructedpicture, reconstructed block, or reconstructed sample array) by addingthe obtained residual signal to the prediction signal (predicted blockor predicted sample array) output from the predictor (including interpredictor 332 and/or intra predictor 331). If there is no residual forthe processing target block, such as a case that a skip mode is applied,the predicted block may be used as the reconstructed block.

The adder 340 may be called a reconstructor or a reconstructed blockgenerator. The generated reconstructed signal may be used for the intraprediction of a next block to be processed in the current picture, andas described later, may also be output through filtering or may also beused for the inter prediction of a next picture.

Meanwhile, a luma mapping with chroma scaling (LMCS) may also be appliedin the picture decoding process.

The filter 350 may improve subjective/objective image quality byapplying filtering to the reconstructed signal. For example, the filter350 may generate a modified reconstructed picture by applying variousfiltering methods to the reconstructed picture, and store the modifiedreconstructed picture in the memory 360, specifically, in a DPB of thememory 360. The various filtering methods may include, for example,deblocking filtering, a sample adaptive offset, an adaptive loop filter,a bilateral filter, and the like.

The (modified) reconstructed picture stored in the DPB of the memory 360may be used as a reference picture in the inter predictor 332. Thememory 360 may store the motion information of the block from which themotion information in the current picture is derived (or decoded) and/orthe motion information of the blocks in the picture having already beenreconstructed. The stored motion information may be transferred to theinter predictor 332 so as to be utilized as the motion information ofthe spatial neighboring block or the motion information of the temporalneighboring block. The memory 360 may store reconstructed samples ofreconstructed blocks in the current picture, and transfer thereconstructed samples to the intra predictor 331.

In the present document, the embodiments described in the filter 260,the inter predictor 221, and the intra predictor 222 of the encodingapparatus 200 may be applied equally or to correspond to the filter 350,the inter predictor 332, and the intra predictor 331.

FIG. 4 illustrates an example of a schematic picture decoding procedureto which an embodiment of the present document is applicable.

In image/video coding, a picture constituting image/video may beencoded/decoded in accordance with a series of decoding orders. Apicture order corresponding to an output order of a decoded picture maybe configured different from the decoding order, and based on this, notonly forward prediction but also backward prediction may be performedduring inter prediction.

In FIG. 4 , S400 may be performed by the entropy decoder 310 of thedecoding apparatus as described above in FIG. 3 , S410 may be performedby the predictor 330, S420 may be performed by the residual processor320, S430 may be performed by the adder 340, and S440 may be performedby the filter 350. S400 may include an information decoding proceduredescribed in the present document, S410 may include an inter/intraprediction procedure described in the present document, S420 may includea residual processing procedure described in the present document, S430may include a block/picture reconstruction procedure described in thepresent document, and S440 may include an in-loop filtering proceduredescribed in the present document.

Referring to FIG. 4 , a picture decoding procedure, as indicated in thedescription for FIG. 3 , may schematically include an image/videoinformation obtaining procedure (S400) from the bitstream (throughdecoding), a picture reconstruction procedure (S410 to S430), and anin-loop filtering procedure (S440) for a reconstructed picture. Thepicture reconstruction procedure may be performed based on predictionsamples and residual samples obtained through inter/intra prediction(S410) and residual processing (dequantization and inverse transform forquantized transform coefficients) (S420) explained in the presentdocument. A modified reconstructed picture may be generated through thein-loop filtering procedure for the reconstructed picture generatedthrough the picture reconstruction procedure, and the modifiedreconstructed picture may be output as a decoded picture, and may alsobe stored in the decoded picture buffer or the memory 360 of thedecoding apparatus to be used as a reference picture in the interprediction procedure after the picture decoding. In some cases, thein-loop filtering procedure may be skipped, and in this case, thereconstructed picture may be output as the decoded picture, and may alsobe stored in the decoded picture buffer or the memory 360 of thedecoding apparatus to be used as the reference picture in the interprediction procedure after the picture decoding. As described above, thein-loop filtering procedure (S440) may include the deblocking filteringprocedure, the sample adaptive offset (SAO) procedure, the adaptive loopfilter (ALF) procedure, and/or the bi-lateral filter procedure, and someor all of the procedures may be skipped. Further, one or some of thedeblocking filtering procedure, the sample adaptive offset (SAO)procedure, the adaptive loop filter (ALF) procedure, and/or thebi-lateral filter procedure may be sequentially applied, or all of theprocedures may be sequentially applied. For example, the SAO proceduremay be performed after the deblocking filtering procedure is applied tothe reconstructed picture. Further, for example, the ALF procedure maybe performed after the deblocking filtering procedure is applied to thereconstructed picture. This may also performed in the same manner evenin the encoding apparatus.

FIG. 5 illustrates an example of a schematic picture encoding procedureto which an embodiment of the present document is applicable.

In FIG. 5 , S500 may be performed by the predictor 220 of the encodingapparatus as described above in FIG. 2 , S510 may be performed by theresidual processor 230, and S520 may be performed by the entropy encoder240. The S500 may include the inter/intra prediction procedure explainedin the present document, S510 may include the residual processingprocedure explained in the present document, and S520 may include theinformation encoding procedure explained in the present document.

Referring to FIG. 5 , the picture encoding procedure may schematicallyinclude not only the procedure of encoding information for picturereconstruction (e.g., prediction information, residual information, andpartitioning information) as represented in the explanation for FIG. 2to output the encoded information in the form of a bitstream, but alsothe procedure of generating the reconstructed picture for the currentpicture and the procedure (optional) of applying the in-loop filteringto the reconstructed picture. The encoding apparatus may derive(modified) residual samples from quantized transform coefficientsthrough the dequantizer 234 and the inverse transformer 235, and maygenerate the reconstructed picture based on the prediction samples beingoutput in S500 and the (modified) residual samples. The reconstructedpicture generated as above may be the same as the reconstructed picturegenerated in the above-described decoding apparatus. The modifiedreconstructed picture may be generated through the in-loop filteringprocedure for the reconstructed picture, and may be stored in thedecoded picture buffer or the memory 270, and in the same manner as inthe decoding apparatus, the modified reconstructed picture may be usedas the reference picture in the inter prediction procedure during thepicture encoding. As described above, in some cases, some or all of thein-loop filtering procedures may be skipped. In case that the in-loopfiltering procedures are performed, (in-loop) filtering relatedinformation (parameter) may be encoded in the entropy encoder 240, andmay be output in the form of the bitstream, and the decoding apparatusmay perform the in-loop filtering procedures in the same method as inthe encoding apparatus based on the filtering related information.

Through the above in-loop filtering procedures, noise, such as blockingartifact and ringing artifact, occurring during image/video coding canbe reduced, and the subjective/objective visual quality can be enhanced.Further, by performing the in-loop filtering procedure in both theencoding apparatus and the decoding apparatus, the same predictionresult can be derived in the encoding apparatus and the decodingapparatus, and thus the picture coding reliability can be enhanced, andthe amount of data to be transmitted for the picture coding can bereduced.

As described above, in not only the decoding apparatus but also theencoding apparatus, the picture reconstruction procedure may beperformed. A reconstructed block may be generated based on intraprediction/inter prediction in each block unit, and a reconstructedpicture including reconstructed blocks may be generated. In case thatthe current picture/slice/tile group is an I picture/slice/tile group,blocks included in the current picture/slice/tile group may bereconstructed based on only the intra prediction. Meanwhile, in casethat the current picture/slice/tile group is a P or B picture/slice/tilegroup, the blocks included in the current picture/slice/tile group maybe reconstructed based on the intra prediction or the inter prediction.In this case, the inter prediction may be applied for some blocks in thecurrent picture/slice/tile group, and the intra prediction may beapplied for the remaining other blocks. Color components of the picturemay include luma components and chroma components, and unless beingexplicitly constrained in the present document, methods and embodimentsproposed in the present document may be applied to the luma componentsand the chroma components.

FIG. 6 exemplarily shows a hierarchical structure for a codedimage/video.

Referring to FIG. 6 , the coded image/video is divided into VCL (videocoding layer) that deals with an image/video decoding process anditself, a subsystem that transmits and stores the coded information, anda network abstraction layer (NAL) that exists between the VCL andsubsystems and is responsible for network adaptation functions.

The VCL may generate VCL data including compressed image data (slicedata), or generate parameter sets including a picture parameter set(Picture Parameter Set: PPS), a sequence parameter set (SequenceParameter Set: SPS), a video parameter set (Video Parameter Set: VPS)etc. or a supplemental enhancement information (SEI) messageadditionally necessary for the decoding process of an image.

In the NAL, a NAL unit may be generated by adding header information(NAL unit header) to a raw byte sequence payload (RBSP) generated in theVCL. In this case, the RBSP refers to slice data, parameter sets, SEImessages, etc. generated in the VCL. The NAL unit header may include NALunit type information specified according to RBSP data included in thecorresponding NAL unit.

As shown in the figure, the NAL unit may be divided into a VCL NAL unitand a Non-VCL NAL unit according to the RBSP generated in the VCL. TheVCL NAL unit may mean a NAL unit including information (sliced data)about an image, and the Non-VCL NAL unit may mean a NAL unit containinginformation (parameter set or SEI message) necessary for decoding animage.

The above-described VCL NAL unit and Non-VCL NAL unit may be transmittedthrough a network by attaching header information according to a datastandard of the subsystem. For example, the NAL unit may be transformedinto a data form of a predetermined standard such as H.266/VVC fileformat, Real-time Transport Protocol (RTP), Transport Stream (TS), etc.and transmitted through various networks.

As described above, in the NAL unit, the NAL unit type may be specifiedaccording to the RBSP data structure included in the corresponding NALunit, and information on this NAL unit type may be stored and signaledin the NAL unit header.

For example, the NAL unit may be roughly classified into the VCL NALunit type and the Non-VCL NAL unit type depending on whether the NALunit includes information about the image (slice data). The VCL NAL unittype may be classified according to property and a type of a pictureincluded in the VCL NAL unit, and the Non-VCL NAL unit type may beclassified according to the type of a parameter set.

The following is an example of the NAL unit type specified according tothe type of parameter set included in the Non-VCL NAL unit type.

-   -   DCI (Decoding Capability Information) NAL unit: Type for NAL        unit including DCI    -   VPS (Video Parameter Set) NAL unit: Type for NAL unit including        VPS    -   SPS (Sequence Parameter Set) NAL unit: Type for NAL unit        including SPS    -   PPS (Picture Parameter Set) NAL unit: Type for NAL unit        including PPS    -   APS (Adaptation Parameter Set) NAL unit: Type for NAL unit        including APS    -   PH (Picture header) NAL unit: Type for NAL unit including PH

The above-described NAL unit types have syntax information for the NALunit type, and the syntax information may be stored and signaled in theNAL unit header. For example, the syntax information may benal_unit_type, and NAL unit types may be specified by a nal_unit_typevalue.

Meanwhile, as described above, one picture may include a plurality ofslices, and one slice may include a slice header and slice data. In thiscase, one picture header may be further added to a plurality of slices(a slice header and a slice data set) in one picture. The picture header(picture header syntax) may include information/parameters commonlyapplicable to the picture. The slice header (slice header syntax) mayinclude information/parameters commonly applicable to the slice. The APS(APS syntax) or PPS (PPS syntax) may include information/parameterscommonly applicable to one or more slices or pictures. The SPS (SPSsyntax) may include information/parameters commonly applicable to one ormore sequences. The VPS (VPS syntax) may include information/parameterscommonly applicable to multiple layers. The DCI (DCI syntax) may includeinformation/parameters related to decoding capability.

In the present document, a high level syntax (HLS) may include at leastone of the APS syntax, PPS syntax, SPS syntax, VPS syntax, decodingcapability information (DCI) syntax, picture header syntax, and sliceheader syntax. Meanwhile, in the present document, a low level syntax(LLS) may include, for example, a slice data syntax, CTU syntax, codingunit syntax, and transform unit syntax.

In the present document, the image/video information being encoded andsignaled in the form of the bitstream from the encoding apparatus to thedecoding apparatus may include not only partitioning related informationin a picture, intra/inter prediction information, residual information,and in-loop filtering information, but also the slice headerinformation, picture header information, APS information, PPSinformation, SPS information, VPS information, and/or DCI information.Further, the image/video information may further include generalconstraint information and/or NAL unit header information.

Meanwhile, as described information, the video/image information of thepresent document may include high level signaling, and the video/imagecoding method may be performed based on the video/image information.

The coded picture may include one or more slices. Parameters describingthe coded picture may be signaled in the picture header, and parametersdescribing the slice may be signaled in the slice header. The pictureheader (PH) is carried in its own NAL unit type. The slice header ispresent in a starting part of a NAL unit including a payload of theslice (slice data).

Further, the picture may be divided into subpictures, tiles, and/orslices. The signaling for the subpictures is present in the SPS, thesignaling for the tile and a rectangular slice is present in the PPS,and lastly, the signaling for a raster scan slice is present in theslice header.

Meanwhile, signaling of profile, tier, and level information may bepresent in the VPS and/or the SPS as in the following Table 1 and Table2.

TABLE 1 Descriptor video_parameter_set_rbsp( ) { vps_video_parameter_set_id u(4)  vps_max_layers_minus1 u(6) vps_max_sublayers_minus1 u(3)  ...  vps_num_ptls_minus1 u(8)  for( i =0; i <= vps_num_ptls_minus1; i++ ) {   if( i > 0 )   vps_pt_present_flag[ i ] u(1)   if(!vps_all_layers_same_num_sublayers_flag )    vps_ptl_max_temporal_id[ i] u(3)  }  while( !byte_aligned( ) )   vps_ptl_alignment_zero_bit /*equal to 0 */ f(1)  for( i = 0; i <= vps_num_ptls_minus1; i++ )  profile_tier_level( vps_pt_present_flag[ i ],  vps_ptl_max_temporal_id[ i ] )  for( i = 0; i < TotalNumOlss; i++ )  if( vps_num_ptls_minus1 > 0 &&   vps_num_ptls_minus1 + 1 !=TotalNumOlss )    vps_ols_ptl_idx[ i ] u(8)  ... }

In Table 1, the vps_video_parameter_set_id provides an identifier forthe VPS so as to be referred to in another syntax element. The value ofthe vps_video_parameter_set_id should be larger than 0.

The vps_max_layers_minus1+1 represents the maximum allowed number oflayers in each coded video sequence (VCS) referring to the VPS.

The vps_max_sublayers_minus1 plus 1 represents the maximum number oftemporal sublayers that may be present in the layer of each CVSreferring to the VPS. The value of the vps_max_sublayers_minus1 shouldbe in the range of 0 to 6.

The vps_num_ptls_minus1+1 represents the number of profile_tier_level () syntax structures in the VPS. The value of the vps_num_ptls_minus1should be smaller than the TotalNumOlss representing the number of alloutput layer sets (OLS).

If the value of the vps_pt_present_flag [i] is 1, this represents thatthe profile, tier, and general constraint information are present in thei-th profile_tier_level ( ) syntax structure in the VPS. If the value ofthe vps_pt_present_flag [i] is 0, this represents that the profile,tier, and general constraint information are not present in the i-thprofile_tier_level ( ) syntax structure in the VPS.

The value of the vps_pt_present_flag [0] is inferred as 1. If the valueof the vps_pt_present_flag [i] is 0, it is inferred that the profile,tier, and general constraint information for the i-th profile_tier_level( ) syntax structure in the VPS is the same as that of the (i−1)-thprofile_tier_level ( ) syntax structure in the VPS.

The vps_ptl_max_temporal_id [i] represents TemporalId of the uppermostsublayer expression whereby level information is present in the i-thprofile_tier_level ( ) syntax structure in the VPS. The value of thevps_ptl_max_temporal_id [i] should be present in a range of 0 to thevps_max_sublayers_minus1. If being not present, it is inferred that thevalue of the vps_ptl_max_temporal_id [i] is the same of the value of thevps_max_sublayers_minus1.

The value of the vps_ptl_alignment_zero_bit is equal to 0.

The vps_ols_ptl_idx [i] represents an index of the profile_tier_level () syntax structure that is applied to the i-th OLS in the VPS for aprofile_tier_level ( ) syntax structure list. If being present, thevalue of the vps_ols_ptl_idx [i] should be present in a range of 0 tothe vps_num_ptls_minus1.

If being not present, the value of the vps_ols_ptl_idx [i] is inferredas follows.

-   -   If the value of the vps_num_ptls_minus1 is 0, the value of the        vps_ols_ptl_idx [i] is inferred as 0.    -   Otherwise (if the value of the vps_num_ptls_minus1 is larger        than 0, and the vps_num_ptls_minus1+1 is equal to TotalNumOlss),        the value of the vps_ols_ptl_idx [i] is inferred to be equal to        i.

If the value of the NumLayersInOls [i] is 1, the profile_tier_level ( )syntax structure being applied to the i-th OLS is present even in theSPS being referred to by the layer in the i-th OLS. If the value of theNumLayersInOls [i] is 1, the requirements of bitstream compatibilityshould be a case that the profile_tier_level ( ) syntax structures beingsignaled in the VPS and the SPS for the i-th OLS are the same.

Each profile_tier_level ( ) syntax structure in the VPS should bereferred to within a range of 0 to TotalNumOlss-1 by at least one valuefor i.

TABLE 2 Descriptor seq_parameter_set_rbsp( ) {  sps_seq_parameter_set_idu(4)  sps_video_parameter_set_id u(4)  sps_max_sublayers_minus1 u(3) sps_reserved_zero_4bits u(4)  sps_ptl_dpb_hrd_params_present_flag u(1) if( sps_ptl_dpb_hrd_params_present_flag )   profile tier level( 1, spsmax sublayers minus1 )  ... }

Referring to Table 2, the sps_seq_parameter_set_id provides anidentifier for the SPS so as to be referred to by other syntax elements.

The SPS NAL units share the same value space as that of thesps_seq_parameter_set_id regardless of the value of the nuh_layer_id.

The spsLayerId is called the nuh_layer_id value of a specific SPS NALunit, and the vclLayerId is called the nuh_layer_id value of a specificVCL NAL unit. The specific VCL NAL unit does not refer to the specificNAL unit unless the spsLayerId is smaller than or equal to thevclLayerId, and the nuh_layer_id includes even a layer in which all OLSsdesignated by the VPS including the same layer as that of the vclLayerIdhave the same nuh_kayer_id as that of the spslayerId.

If the value of the sps_video_parameter_set_id is larger than 0, thisrepresents the vps_video_parameter_set_id value for the VPS beingreferred to by the SPS.

If the value of the sps_video_parameter_set_id is 0, the followings areapplied.

-   -   The SPS does not refer to the VPS, and when each coded layer        video sequence (CLVS) referring to the SPS is decoded, the VPS        is not referred to.    -   The value of the vps_max_layers_minus1 is inferred as 0.    -   The value of the vps_max_sublayers_minus1 is inferred as 6.    -   The CVS should include only one layer (i.e., all VCL NAL units        in the CVS have the same nuh_layer_id value).    -   The value of the GeneralLayerIdx [nuh_layer_id] is inferred as        0.    -   The value of the vps_independent_layer_flag [GeneralLayerIdx        [nuh_layer_id]] is inferred as 1.

If the value of the vps_independent_layer_flag [GeneralLayerIdx[nuh_layer_id]] is 1, the SPS being referred to by the CLVS having thenuhLayerId of the specific nuh_layer_id value should have the samenuh_layer_id as that of the nuhLayerId.

The value of the sps_video_parameter_set_id should be the same in allSPSs being referred to by the CLVSs in the CVS.

The sps_max_sublayers_minus1 plus 1 represents the maximum number oftemporal sublayers that can be present in each CLVS referring to theSPS. The value of the sps_max_sublayers_minus1 should be in a range of 0to vps_max_sublayers_minus1.

The sps_reserved_zero_4 bits is equal to 0.

If the value of the sps_ptl_dpb_hrd_params_present_flag is 1, this mayrepresent that the profile_tier_level ( ) syntax structure and thedpb_parameters ( ) syntax structure are present in the SPS, and thegeneral_hrd_parameters ( ) syntax structure and the ols_hrd_parameters () syntax structure are present in the SPS. If the value of thesps_ptl_dpb_hrd_params_present_flag is 0, this represents that the foursyntax structures as described above are not present in the SPS.

If the value of the sps_video_parameter_set_id is larger than 0 and theOLS, in which the nuh_layer_id includes only one layer that is the sameas that of the nuh_layer_id of the SPS, is present, or the value of thesps_video_parameter_set_id is 0, the value of thesps_ptl_dpb_hrd_params_present_flag is the same as 1.

Meanwhile, the syntax structure of the PTL (profile, tier, level)information may be as follows.

TABLE 3 Descriptor profile_tier_level( profileTierPresentFlag,maxNumSubLayersMinus1 ) {  if( profileTierPresentFlag ) {  general_profile_idc u(7)   general_tier_flag u(1)  general_constraint_info( )  }  general_level_idc u(8)  if(profileTierPresentFlag ) {   ptl_num_sub_profiles u(8)   for( i = 0; i <ptl_num_sub_profiles; i++ )    general_sub_profile_idc[ i ] u(32)  } for( i = 0; i < maxNumSubLayersMinus1; i++ )  ptl_sublayer_level_present_flag[ i ] u(1)  while( !byte_aligned( ) )  ptl_alignment_zero_bit f(1)  for( i = 0; i < maxNumSubLayersMinus1;i++ )   if( ptl_sublayer_level_present_flag[ i ] )   sublayer_level_idc[ i ] u(8) }

Referring to Table 3, the profile_tier_level ( ) syntax structureprovides level information, and selectively provide the profile, tier,sub-profile, and general constraint information.

If the profile_tier_level ( ) syntax structure is included in the VPS,the OlsInScope is one or more OLSs specified by the VPS. If theprofile_tier_level ( ) syntax structure is included in the SPS, theOlsInScope is the OLS including only the lowermost layer among thelayers referring to the SPS, and the lowermost layer is an independentlayer.

The general_profile_idc represent the profile with which the OlsInScopecomplies.

The general_tier_flag represents a tier context for interpretation ofthe general_level_idc.

The general_level_idc represents the level with which the OlsInScopecomplies.

As the value of the general_level_idc becomes larger, a higher level isrepresented. The maximum level being signaled in the DCI NAL unit forthe OlsInScope may be higher than the level being signaled in the SPSfor the CLVS included in the OlsInScope, but cannot be lower than thesame.

In case that the OlsInScope complies with several profiles, thegeneral_profile_idc represents the profile providing the preferreddecoding result or the preferred bitstream identification as determinedby the encoding apparatus.

In case that the CVSs of the OlsInScope conform with different profiles,several profile_tier_level ( ) syntax structures may be included in theDCI NAL unit so that at least one set of the profile, tier, and levelfor the decoding apparatus that can decode each CVS of the OlsInScope ispresent.

The num_sub_profiles represents the number of general_sub_profile_idc[i] syntax elements.

The general_sub_profile_idc [i] represents the i-th interoperabilitymetadata.

If the value of the sublayer_level_present_flag [i] is 1, thisrepresents that the level information is present in theprofile_tier_level ( ) syntax element for expression of the sublayer inwhich the TemporalId is i. If the value of thesublayer_level_present_flag [i] is 0, this represents that the levelinformation is not present in the profile_tier_level ( ) syntaxstructure for the expression of the sublayer in which the TemporalId isi.

The value of the ptl_alignment_zero_bits is the same as 0.

The semantics of the syntax element of the sublayer_level_idc [i] arethe same as those of the general_level_idc syntax element, but areapplied to the expression of the sublayer in which the TemporalId is i.

In case of being not present, the value of the sublayer_level_idc [i] isinferred as follows.

-   -   The sublayer_level_idc [maxNumSubLayersMinus1] is inferred to be        the same as the general_level_idc having the same        profile_tier_level ( ) structure.    -   In the maxNumSubLayersMinus1−1, the sublayer_level_idc [i] is        inferred to be the same as the sublayer_level_idc [i+1] with        respect to i in the range including 0 (descending order of i        value).

For reference, the sublayer may represent a temporal scalable layer of atemporal scalable bitstream composed of VCL NAL units having aTemporalId variable of a specific value and related non-VCL NAL units.The sublayer expression may be a subset of bitstream composed of NALunits of a specific sublayer and lower sublayers.

The general_constraint_info ( ) may include the following syntaxelements.

TABLE 4 Descriptor general_constraint_info( ) { general_non_packed_constraint_flag u(1) general_frame_only_constraint_flag u(1) general_non_projected_constraint_flag u(1) general_one_picture_only_constraint_flag u(1) intra_only_constraint_flag u(1)  max_bitdepth_constraint_idc u(4) max_(——)chroma_format_constraint_idc u(2)  single_layer_constraint_flagu(1)  all_layers_independent_constraint_flag u(1) no_ref_pic_resampling_constraint_flag u(1) no_res_change_in_clvs_constraint_flag u(1) one_tile_per_pic_constraint_flag u(1) pic_header_in_slice_header_constraint_flag u(1) one_slice_per_pic_constraint_flag u(1) one_subpic_per_pic_constraint_flag u(1) no_qtbtt_dual_tree_intra_constraint_flag u(1) no_partition_constraints_override_constraint_flag u(1) no_sao_constraint_flag u(1)  no_alf_constraint_flag u(1) no_ccalf_constraint_flag u(1)  no_joint_cbcr_constraint_flag u(1) no_mrl_constraint_flag u(1)  no_isp_constraint_flag u(1) no_mip_constraint_flag u(1)  no_ref_wraparound_constraint_flag u(1) no_temporal_mvp_constraint_flag u(1)  no_sbtmvp_constraint_flag u(1) no_amvr_constraint_flag u(1)  no_bdof_constraint_flag u(1) no_dmvr_constraint_flag u(1)  no_cclm_constraint_flag u(1) no_mts_constraint_flag u(1)  no_sbt_constraint_flag u(1) no_lfnst_constraint_flag u(1)  no_affine_motion_constraint_flag u(1) no_mmvd_constraint_flag u(1)  no_smvd_constraint_flag u(1) no_prof_constraint_flag u(1)  no_bcw_constraint_flag u(1) no_ibc_constraint_flag u(1)  no_ciip_constraint_flag u(1) no_gpm_constraint_flag u(1)  no_ladf_constraint_flag u(1) no_transform_skip_constraint_flag u(1)  no_bdpcm_constraint_flag u(1) no_palette_constraint_flag u(1)  no_act_constraint_flag u(1) no_lmcs_constraint_flag u(1)  no_cu_qp_delta_constraint_flag u(1) no_chroma_qp_offset_constraint_flag u(1)  no_dep_quant_constraint_flagu(1)  no_sign_data_hiding_constraint_flag u(1)  no_tsrc_constraint_flagu(1)  no_mixed_nalu_types_in_pic_constraint_flag u(1) no_trail_constraint_flag u(1)  no_stsa_constraint_flag u(1) no_rasl_constraint_flag u(1)  no_radl_constraint_flag u(1) no_idr_constraint_flag u(1)  no_cra_constraint_flag u(1) no_gdr_constraint_flag u(1)  no_aps_constraint_flag u(1)  while(!byte_aligned( ) )   gci_alignment_zero_bit f(1)  gci_num_reserved_bytesu(8)  for( i = 0; i < gci_num_reserved_bytes; i+− )   gci_reserved_byte[i ] u(8) }

Referring to Table 3, signaling of a level indicator (i.e.,general_level_idc) is present after signaling of general constraintinformation (general_constraint_info). Accordingly, if generalconstraint information is present in the PTL information, the decodingapparatus should first parse the general constraint information, andthus parsing of the level indicator becomes complicated. Further, sincethe general constraint information may not be necessary in the decodingapparatus, the decoding apparatus may desire to skip the parsing of thegeneral constraint information. However, according to Table 3, if thegeneral constraint information is present in the PTL information, theparsing thereof is unable to be skipped.

Further, the signaling of the general constraint information is alwayspresent in the PTL information when the value of theprofileTierPresentFlag is 1. However, the general constraint informationdoes not always have to be present in the PTL information when theprofile, tier, and level information are present. Accordingly, there isa need for a mechanism not to signal the general constraint informationeven in case that the PTL information is present.

Further, the signaling of the general constraint information is presentin the middle of the signal of the profile, tier, and level information.This imposes a burden on decoding information to process the profile,tier, and level information separately from the processing of thegeneral constraint information.

The following drawings have been prepared to explain a specific exampleof the present document. The name of a specific device described in thedrawings or the number of a specific signal/information has beenexemplarily presented, and thus the technical feature of the presentspecification is not limited to the specific name used in the followingdrawings.

In order to solve the above-described problems, the present documentprovides the following methods. The respective methods may be appliedindependently or in combination.

1. In the profile, tier, and level structure (PTL structure), a levelindicator may be signaled before a syntax element whose presence isconditioned. For example, In the PTL information, the general_level_idcmay be signaled prior to the general_profile_idc.

2. A flag representing whether flag(s) being signaled for the generalconstraint information (GCI) are present may be added. This flag may becalled a gci_present_flag. The flag(s) for the general constraintinformation include syntax elements specified in Table 4 and those yetto be reserved.

3. The total number of bits for general constraint information includingthe gci_present_flag is designated in the unit of a byte (i.e., thenumber of bits is a multiple of 8).

4. The bits reserved for a general constraint flag starts at abyte-aligned position. As a result, there may be some bits being presentfor byte alignment before reserved bits are present.

5. In addition to a new flag gci_present_flag, a syntax elementrepresenting the number of reserved bytes in a GCI structure may bechanged to represent the number of general constraint flag (includingreserved bit and flag), and may be first signaled just below thegci_present_flag in the GCI structure. The syntax element may be calledgci_num_constraint_bytes. If the value of the gci_present_flag is 0, thevalue of the gci_num_constraint_bytes is 0. The number of bits forsignaling of the gci_present_flag and the gci_num_constraint_bytes maybe byte-aligned. For example, the number of bits for signaling of thegci_num_constraint_bytes may become 7.

6. As an alternative for Item 4, it is not necessary for the reservedbits for the general constraint flag to start at the byte-alignedposition. As a result, this eliminates the need to have the byte-alignedbit before the presence of the reserved bits.

7. As an alternative for Item 1, the profile, tier, and levelinformation may be signaled in a method in which they are not separatedby other syntax elements. This may be implemented by moving thesignaling of the general constraint information to the position afterthe signaling of the level information.

8. As an alternative for Item 5, the signaling of thegci_num_constraint_bytes may replace the gci_present_flag without beingadded to the gci_present_flag.

9. The syntax structure (general_constraint_info ( )) of the generalconstraint information is present in the profile tier level structure(profile_tier_level syntax) after signaling of the profile, tier, andlevel information including the profile, tier, and level information forthe sublayers.

10. In case that the syntax structure of the general constraintinformation is present in the end of the profile tier level structure,the size of the general constraint information may or may not bebyte-aligned.

As an embodiment, the encoding apparatus may signal theprofile_tier_level syntax having the structure of the following Table 5,and semantics therefor may be as in the following Table 6.

TABLE 5 Descriptor profile_tier_level( profileTierPresentFlag,maxNumSubLayersMinus1 ) {  general_level_idc u(8)  if(profileTierPresentFlag ) {   general_profile_idc u(7)  general_tier_flag u(1)   general_constraint_info( )  ptl_num_sub_profiles u(8)   for( i = 0; i < ptl_num_sub_profiles; i++)    general_sub_profile_idc[ i ] u(32)  }  ... }

TABLE 6 general_level_idc indicates a level to which OlsInScope conformsas specified in Annex A. Bitstreams shall not contain values ofgeneral_level_idc other than those specified in Annex A. Other values ofgeneral_level_idc are reserved for future use by ITU-T | ISO/IEC.  NOTE1 - A greater value of general_level_idc indicates a higher level. Themaximum level signalled in the DCI NAL unit  for OlsInScope may behigher than but cannot be lower than the level signalled in the SPS fora CLVS contained within  OlsInScope.  NOTE 2 - When OlsInScope conformsto multiple profiles, general_profile_idc should indicate the profilethat provides the  preferred decoded result or the preferred bitstreamidentification, as determined by the encoder (in a manner not specifiedin  this Specification).  NOTE 3 - When the CVSs of OlsInScope conformto different profiles, multiple profile_tier_level( ) syntax structuresmay be  included in the DCI NAL unit such that for each CVS of theOlsInScope there is at least one set of indicated profile, tier, and level for a decoder that is capable of decoding the CVS.general_profile_idc indicates a profile to which OlsInScope conforms asspecified in Annex A. Bitstreams shall not contain values ofgeneral_profile_idc other than those specified in Annex A. Other valuesof general_profile_idc are reserved for future use by ITU-T | ISO/IEC.general_tier_flag specifies the tier context for the interpretation ofgeneral_level_idc as specified in Annex A.

Referring to Table 5 and Table 6, the general_level_idc represents thelevel with which the OlsInScope complies. As the value of thegeneral_level_idc becomes larger, a higher level is represented. Themaximum level being signaled in the DCI NAL unit for the OlsInScope maybe higher than the level being signaled in the SPS for the CLVS includedin the OlsInScope, but cannot be lower than the same. In case that theOlsInScope complies with several profiles, the general_profile_idcrepresents the profile providing the preferred decoding result or thepreferred bitstream identification as determined by the encodingapparatus. In case that the CVSs of the OlsInScope conform to differentprofiles, several profile_tier_level syntax structures may be includedin the DCI NAL unit so that at least one set of the profile, tier, andlevel for the decoding apparatus that can decode the CVS with respect tothe respective CVSs of the OlsInScope is present.

The general_profile_idc represents the profile with which the OlsInScopecomplies.

The general_tier_flag represents a tier context for interpretation ofthe general_level_idc.

The general constraint information (general_constraint_info) may bepresent next to the profile information (general_profile_idc), the tierinformation (general_tier_flag), and the level information(general_level_idc) in the profile_tier_level syntax structure of Table3. Accordingly, the decoding apparatus may separately process thegeneral constraint information after processing the profile, tier, andlevel information.

Meanwhile, as an example, the encoding apparatus may signal thegeneral_constraint_info syntax having the structure as in the followingTable 7.

TABLE 7 Descriptor general_constraint_info( ) {  gci_present_flag u(1) if( gci_present_flag ) {   general_non_packed_constraint_flag u(1)  ... u(1)   no_aps_constraint_flag u(1)   gci_num_reserved_bytes u(8) }  while( ! byte_aligned( ) )   gci_alignment_zero_bit f(1)  for( i =0; i < gci_num_reserved_bytes; i++ )   gci_reserved_byte[ i ] u(8) }

In Table 7, the gci_present_flag represents whether information(general_non_packed_constraint_flag and the like) on the constraints ispresent in the general_constraint_info syntax (general constraintinformation).

The gci_num_reserved_bytes represents the number of bytes reserved forthe general constraint information.

The gci_alignment_zero_bit is information for byte alignment, and hasthe value of 0.

The gci_reserved_byte[i] represents the bytes reserved for the generalconstraint information. The gci_reserved_byte[i] does not exert aninfluence on the decoding process, and may have a certain value.

For example, the semantics for the gci_present_flag may be as in thefollowing Table 8.

TABLE 8 gci_present_flag equal to 1 specifies that the generalconstraint flags are present in the profile_tier_level( ) syntaxstructure when profileTierPresenfFlag is equal to 1. gci_present_flagequal to 0 specifies, that the general constraint flags are not presentin the profile_tier_level( ) syntax structure. When gci_present_flagequal to 0 for a profile_tier_level( ) syntax structure withprofileTierPresentFlag equal to 1, the value ofmax_bitdepth_constraint_idc is inferred to be equal to 8, the vlaue ofmax_chroma_format_constraint_idc is inferred to be equal to 3, and thevalue of the each of the other syntax elements in thegeneral_constraint_info( ) syntax structure starting fromgeneral_non_packed_constraint_flag to no_aps_constraint_flag, inclusive,is inferred to be equal to 0.

Referring to Table 8, if the value of the gci_present_flag is 1, thisrepresents that the general constraint information (flag) is present inthe profile_tier_level syntax in case that the value of theprofileTierPresentFlag is 1. If the value of the gci_present_flag is 0,this represents that the general constraint information is not presentin the profile_tier_level syntax.

If the value of the gci_present_flag is 0 for the profile_tier_levelsyntax in which the value of the profileTierPresentFlag is 1, it isinferred that the value of the max_bitdepth_constraint_idc is 8, and thevalue of the max_chroma_format_constraint_idc is 3. Further, it isinferred that the value of other syntax elements (from thegeneral_non_packed_constraint_flag to the no_aps_constraint_flag) in thegeneral_constraint_info syntax is 0.

Accordingly, if the general constraint information is not necessary forcoding of the image information, the encoding apparatus may encode thevalue of the gci_present_flag as 0, and the decoding apparatus may skipparsing of the general constraint information in case that the value ofthe gci_present_flag is 0.

As another example, the encoding apparatus may signal thegeneral_constraint_info syntax having the structure of the followingTable 9.

TABLE 9 Descriptor general_constraint_info( ) {  gci_present_flag u(1) gci_num_constraint_bytes u(7)  if( gci_present_flag ) {  general_non_packed_constraint_flag u(1)   ... u(1)  no_aps_constraint_flag u(1)   while( ! byte_aligned( ) )   gci_alignment_zero_bit f(1)   for( i = 0; i <gci_num_reserved_bytes −9; i++ )    gci_reserved_byte[ i ] u(8)  } }

In Table 9, the semantics for the gci_present_flag may be as in Table 8,and the semantics for the gci_num_constraint_bytes may be as in thefollowing Table 10.

TABLE 0 gci_num_constraint_bytes specifies the length in bytes of thegeneral constraint flags including the reserved bits, not including thebyte used for signalling gci_present_flag and gci_num_constraint_bytesthemselves. The value of gci_num_constraint_bytes shall be equal to 0 orequal to 9. Other values of gci_num_constraint_bytes are reserved forfuture use by ITU-T | ISO/IEC and shall not be present in bitstreamsconforming to this version of this Specification. When the value ofgci_present_flag is equal to 0, the value of gci_num_constraint_bytesshall be equal to 0. Otherwise (i.e., the value of gci_present_flag isnot equal to 0), the value of gci_num_constraint_bytes shall not be lessthan 9. NOTE - The value 9 may be changed when the number of specifiedgeneral constraint flags changes.

Referring to Table 10, the gci_num_constraint_bytes does not includebytes being used to signal the gbi_present_flag and thegci_num_constraint_bytes, and represents the length of the generalconstraint flags including the reserved bits in the unit of a byte. Thevalue of the gci_num_constraint_bytes is 0 or 9. If the value of thegci_present_flag is 0, the value of the gci_num_constraints_bytes is 0.If the value of the gci_present_flag is not 0, the value of thegci_num_constraint_bytes should not be smaller than 9. In case that thenumber of general constraint flags (information on the generalconstraint) is changed in signaling the general constraint information,the value of the gi_num_constraint_bytes may be changed to 9.

As another example, the encoding apparatus may signal thegeneral_constraint_info syntax having the structure as in the followingTable 11.

TABLE 11 Descriptor general_constraint_info( ) {  gci_present_flag u(1) gci_num_constraint_bytes u(7)  if( gci_present_flag ) {  general_non_packed_constraint_flag u(1)   ... u(1)  no_aps_constraint_flag u(1)   for( i = numSpecifiedFlags; i <  (gci_num_reserved_bytes * 8); i++ )    gci_reserved_bit[ i ] u(1)  } }

In Table 11, the value of the numSpecifiedFlags represents the number ofspecified (unreserved) general constraint flags. This value is 66 (i.e.,the number of flags from the general_non_packed_constraint_flag to theno_aps_constraint_flag).

The semantics for the gci_present_flag and the gci_num_constraint_bytesmay be as in Table 8 and Table 10, and the semantics for thegci_reserved_bit[i] may be as in the following Table 12.

TABLE 12 gci_reserved_bit[ i ] may have any value. Its presence andvalue do not affect decoder conformance to profiles specified in thisversion of this Specification. Decoders conforming to this version ofthis Specification shall ignore the values of all the gci_reserved_bit[i ] syntax elements.

Referring to Table 12, the value of the gci_reserved_bit[i] is the valuethat does not exert an influence on the decoding process, and may have acertain value.

Meanwhile, as another embodiment, the encoding apparatus may signal theprofile_tier_level syntax having the structure as in the following Table13.

TABLE 13 Descriptor profile_tier_level( profileTierPresentFlag,maxNumSubLayersMinus1 ) {  if( profileTierPresentFlag ) {  general_profile_idc u(7)   general_tier_flag u(1)  } general_level_idc u(8)  if( profileTierPresentFlag ) {  general_constraint_info( )   ptl_num_sub_profiles u(8)   for( i = 0; i< ptl_num_sub_profiles; i++ )    general_sub_profile_idc[ i ] u(32)  } ... }

Referring to Table 13, the level information (general_level_idc) in theprofile_tier_level syntax may be signaled next to the profileinformation (general_profile_idc) and the tier information(general_tier_flag), and the general constraint information(general_constraint_info) may be signaled next to the level information.

In this case, the encoding apparatus may signal thegeneral_constraint_info syntax having the structure as in the followingTable 14 or Table 15.

TABLE 14 Descriptor general_constraint_info( ) {  gci_present_flag u(1) gci_num_constraint_bytes u(7)  if( gci_present_flag ) {  general_non_packed_constraint_flag u(1)   ... u(1)  no_aps_constraint_flag u(1)   for( i = numSpecifiedFlags;   i < (gcinum reserved bytes * 8); i++ )    gci_reserved_bit[ i | u(1)  } }

TABLE 15 Descriptor general_constraint_info( ) { gci_num_constraint_bytes u(8)  if( gci_num_constraint_bytes > 0 ) {  general_non_packed_constraint_flag u(1)   ... u(1)  no_aps_constraint_flag u(1)   for( i = numSpecifiedFlags;   i <(gci_num_reserved_bytes * 8); i++ )    gci_reserved_bit[ i ] u(1)  } }

In Table 15, the gci_num_constraint_bytes represents the number ofreserved bytes for information (general constraint_flag) on theconstraints, does not include the bytes being used to signal thegci_num_constraint_bytes, and represents the length of the generalconstraint flags including the reserved bits in the unit of a byte. Thevalue of the gci_num_constraint_bytes is 0 or 9.

The gci_reserved_bit[i] may be parsed in the general_constraint_infosyntax based on the value of the gci_num_constraint_bytes.

As still another embodiment, the encoding apparatus may signal theprofile_tier_level syntax having the structure as in the following Table16.

TABLE 16 Descriptor profile_tier_level( profileTierPresentFlag,maxNumSubLayersMinus1 ) {  if( profileTierPresentFlag ) {  general_profile_idc u(7)   general_tier_flag u(1)  } general_level_idc u(8)  if( profileTierPresentFlag ) {  ptl_num_sub_profiles u(8)   for( i = 0; i < ptl_num_sub_profiles; i++)    general_sub_profile_idc[ i ] u(32)  }  for( i = 0; i <maxNumSubLayersMinus1; i++ )   ptl_sublayer_level_present_flag[ i ] u(1) while( !byte_aligned( ) )   ptl_alignment_zero_bit f(1)  for( i = 0; i< maxNumSubLayersMinus1; i++ )   if( ptl_sublayer_level_present_flag[ i] )    sublayer_level_idc[ i ] u(8)  if( profileTierPresentFlag )  general_constraint_info( ) }

Referring to Table 16, the general constraint information may beincluded in the end of the profile_tier_level syntax.

In this case, the encoding apparatus may signal thegeneral_constraint_info syntax having the structure as in the followingTable 17 to Table 19.

TABLE 17 Descriptor general_constraint_info( ) {  gci_present_flag u(1) if( gci_present_flag ) {   general_non_packed_constraint_flag u(1)  ... u(1)   no_aps_constraint_flag u(1)   gci_num_reserved_bits u(8)  for( i = 0; i < gci_num_reserved_bits; i++ )    gci_reserved_bit[ i ]u(1)  }  while( !byte_aligned( ) )   gci_alignment_zero_bit f(1) }

TABLE 18 Descriptor general_constraint_info( ) {  gci_present_flag u(1) if( gci_present_flag) {   general_non_packed_constraint_flag u(1)   ...u(1)   no_aps_constraint_flag u(1)   gci_num_reserved_bytes u(8)   for(i = 0; i < gci_num_reserved_bytes; i++ )    gci_reserved_byte[ i ] u(8) }  while( !byte_aligned( ) )   gci_alignment_zero_bit f(1) }

TABLE 19 Descriptor general_constraint_info( ) {  gci_present_flag u(1) if( gci_present_flag ) {   general_non_packed_constraint_flag u(1)  ... u(1)   no_aps_constraint_flag u(1)   while( !byte_aligned( ) )   gci_alignment_zero_bit f(1)   gci_num_reserved_bytes u(8)   for( i =0; i < gci_num_reserved_bytes; i ++ )    gci_reserved_byte[ i ] u(8)  } while( !byte_aligned( ) )   gci_alignment_zero_bit f(1) }

In Table 17, the gci_num_constraint_bits represents the number of bitsreserved for the information (general constraint flag) on the generalconstraint. The gci_reserved_bit[i] may be parsed in thegeneral_constraint_info syntax based on the value of thegci_num_constraint_bits.

Referring to Table 17 to Table 19, the alignment information(gci_alignment_zero_bit) may be present in the end in thegeneral_constraint_info syntax. In other words, the alignmentinformation may be included next to number information(gci_num_constraint_bits or gci_num_constraint_bytes) on the bitsreserved for the general constraint information in thegeneral_constraint_info syntax and the reserved bits(gci_reserved_bit[i] or gci_reserved_byte[i]).

As still another embodiment, the encoding apparatus may signal theprofile_tier_level syntax having the structure as in the following Table20.

TABLE 20 Descriptor profile_tier_level( profileTierPresentFlag,maxNumSubLayersMinus1 ) {  if( profileTierPresentFlag ) {  general_profile_idc u(7)   general_tier_flag u(1)  } general_level_idc u(8)  if( profileTierPresentFlag ) {  ptl_num_sub_profiles u(8)   for( i = 0; i < ptl_num_sub_profiles; i++)    general_sub_profile_idc[ i ] u(32)  }  for( i = 0; i <maxNumSubLayersMinus1; i++ )   ptl_sublayer_level_present_flag[ i ] while( !byte_aligned( ) )   ptl_alignment_zero_bit f(1)  for( i = 0; i< maxNumSubLayersMinus1; i++ )   if( ptl_sublayer_level_present_flag[ i] )    sublayer_level_idc[ i ] u(8)  if( profileTierPresentFlag )  general_constraint_info( ) }

Referring to Table 20, the general constraint information may be presentin the end in the profile_tier_level syntax. In other words, the generalconstraint information may be signaled next to the profile information(general_profile_idc), tier information (general_tier_flag), and levelinformation (general_level_idc) in the profile_tier_level syntax.

In this case, the encoding apparatus may signal thegeneral_constraint_info syntax having the structure as in the followingTable 21 to Table 24.

TABLE 21 Descriptor general_constraint_info( ) {  gci_present_flag u(1) if( gci_present_flag ) {   general_non_packed_constraint_flag u(1)  ... u(1)   no_aps_constraint_flag u(1)   gci_num_reserved_bits u(8)  for( i = 0; i < gci_num_reserved_bits; i++)    gci_reserved_bit[ i ]u(1)  } }

TABLE 22 Descriptor general_constraint_info( ) {  gci_present_flag u(1) if( gci_present_flag ) {   general_non_packed_constraint_flag u(1)  ... u(1)   no_aps_constraint_flag u(1)   while( !byte_aligned( ) )   gci_alignment_zero_bit f(1)   gci_num_reserved_bits u(8)   for( i =0; i < gci_num_reserved_bits; i++)    gci_reserved_bit[ i ] u(1)  } }

TABLE 23 Descriptor general_constraint_info( ) {  gci_present_flag u(1) if( gci_present_flag ) {   general_non_packed_constraint_flag u(1)  ... u(1)   no_aps_constraint_flag u(1)   while( !byte_aligned( ) )   gci_alignment_zero_bit f(1)   gci_num_reserved_bytes u(8)   for( i =0; i < gci_num_reserved_bytes; i++ )    gci_reserved_byte[ i ] u(8)  } }

TABLE 24 Descriptor general_constraint_info( ) {  gci_present_flag u(1) if( gci_present_flag ) {   general_non_packed_constraint_flag u(1)  ...   no_aps_constraint_flag u(1)   gci_num_reserved_bytes u(8)   for(i = 0; i < gci_num_reserved_bytes; i++ )    gci_reserved_byte[ i ] u(8)} }

In Table 21 and Table 22, the gci_num_constraint_bits represents thenumber of bits reserved for the information on the constraint (generalconstraint flag). The gci_reserved_bit[i] may be parsed in thegeneral_constraint_info syntax based on the value of thegci_num_constraint_bits.

Referring to Table 21 to Table 24, the bits or bytes reserved for thegeneral constraint information may be included in the end of thegeneral_constraint_info syntax.

FIGS. 7 and 8 schematically illustrate a video/image encoding method andan example of related components according to an embodiment of thepresent document.

The video/image encoding method disclosed in FIG. 7 may be performed bythe (video/image) encoding apparatus 200 disclosed in FIGS. 2 and 8 . Asan example, S700 and S710 of FIG. 7 may be performed by the predictor220 of the encoding apparatus 200. S720 may be performed by the entropyencoder 240 of the encoding apparatus 200. The video/image encodingmethod disclosed in FIG. 7 may include the embodiments as describedabove in the present document.

Specifically, referring to FIGS. 7 and 8 , the predictor 220 of theencoding apparatus may perform at least one of inter prediction or intraprediction for the current block in the current picture (S700), andbased on this, may generate prediction samples (prediction block) forthe current block and prediction information (S710).

In case that the intra prediction is performed, the predictor 220 maypredict the current block with reference to samples in the currentpicture (neighboring samples of the current block). The predictor 220may determine a prediction mode being applied to the current block usingthe prediction mode applied to the neighboring samples.

In case that the inter prediction is performed, the predictor 220 maygenerate prediction information and a predicted block for the currentblock by performing the inter prediction based on motion information ofthe current block. The above-described prediction information mayinclude information on the prediction mode and information on the motioninformation. The information on the motion information may includecandidate selection information (e.g., merge index, mvp flag, or mvpindex) that is information for deriving a motion vector. Further, theinformation on the motion information may include information on amotion vector difference (MVD) and/or reference picture indexinformation. Further, the information on the motion information mayinclude information representing whether L0 prediction, L1 prediction,or bi-prediction is applied. For example, the predictor 220 may derivethe motion information of the current block in the current picture basedon motion estimation. For this, the predictor 220 may search a highlycorrelated similar reference block in the unit of a fractional pixel ina determined search range in the reference picture using the originalblock in the original picture for the current block, and through this,may derive the motion information. The block similarity may be derivedbased on a difference between phase-based sample values. As an example,the block similarity may be calculated based on a sum of absolutedifference (SAD) between the current block (or template of the currentblock) and the reference block (or template of the reference block). Inthis case, the motion information may be derived based on the referenceblock having the smallest SAD in the search area. The derived motioninformation may be signaled to the decoding apparatus according tovarious methods based on the inter prediction mode.

The residual processor 230 of the encoding apparatus may generateresidual samples and residual information based on the predictionsamples generated by the predictor 220 and the original picture(original block and original samples). Here, the residual information isinformation on the residual samples, and may include information on(quantized) transform coefficients for the residual samples.

The adder (or reconstructor) of the encoding apparatus may generatereconstructed samples (reconstructed picture, reconstructed block, andreconstructed sample array) by adding the residual samples generated bythe residual processor 230 and the prediction samples generated by thepredictor 220 to each other.

The entropy encoder 240 of the encoding apparatus may encode imageinformation including the prediction information generated by thepredictor 220, the residual information generated by the residualprocessor 230, and information on the HLS (S720).

The information on the HLS may include information/syntax for aparameter set being used for decoding of the image/video information. Asan example, the parameter set may include APS, PPS, SPS, VPS, and thelike. The SPS and/or VPS may include PTL information (profile_tier_levelsyntax) as described above in Table 1 and Table 2.

The PTL information may include profile information(general_profile_idc) representing a profile to which output layer setsconform, level information (general_level_idc) representing the level towhich the output layer sets conform, tier context information forinterpretation of the level information, and general constraintinformation for constraints to which the output layer sets conform. Thegeneral constraint information may be simply called constraintinformation.

If the PTL information is included in the VPS, the output layer setsinclude one or more output layer sets specified by the VPS. In case thatthe PTL information is included in the SPS, the output layer set is theoutput layer set including only the lowermost layer among the layersreferring to the SPS.

The encoding apparatus may generate the level information representingthe level to which the output layer sets conform in generating the PTLinformation, and may generate the profile information representing theprofile to which the output layer sets conform, the tier contextinformation for interpretation of the level information, and the generalconstraint information. Here, the general constraint information may bepresent next to the level information in the PTL information(profile_tier_level syntax). That is the level information may be firstpresent prior to the general constraint information in the PTLinformation.

The general constraint information may include a flag (gci_present_flag)representing whether information on the constraints (general constraintflags) is present in the general constraint information. If the value ofthe gci_present_flag is 1, the information on the constraints may beincluded in the general constraint information. If the value of thegci_present_flag is 0, the information on the constraints may not bepresent in the general constraint information.

Meanwhile, the general constraint information may include alignmentinformation (gci_alignment_zero_bit) having the value of 0. Thealignment information may be present next to the number informationrepresenting the number of bits reserved for the information on theconstraints and/or the reserved bits in the general constraintinformation. As an example, the alignment information may be present inthe last position of the general constraint information.

The entropy encoder 240 of the encoding apparatus may encode the imageinformation including the level information, the profile information,the tier information, and/or the general constraint information. Theencoded image information may be transmitted or stored in the form ofthe bitstream in the NAL unit.

According to the present document, since the encoding apparatus may notsignal the general constraint information by configuring the value ofthe gci_present_flag as 0 even in case of signaling the PTL information,it may not signal the general constraint information in case that thegeneral constraint information is unnecessary in the decoding procedure.Further, since the general constraint information is present next to theprofile information, the tier information, and the level information inthe PTL information, the decoding apparatus may process the generalconstraint information separately from the profile, the tier, and thelevel information.

FIGS. 9 and 10 schematically illustrate a video/image decoding methodand an example of related components according to an embodiment of thepresent document.

The video/image decoding method disclosed in FIG. 9 may be performed bythe (video/image) decoding apparatus 300 disclosed in FIGS. 3 and 10 .Specifically, for example, S900 to S920 of FIG. 9 may be performed bythe entropy decoder 310 of the decoding apparatus. S940 may be performedby the residual processor 320, the predictor 330, and the adder 340 ofthe decoding apparatus. The video/image decoding method disclosed inFIG. 9 may include the above-described embodiments.

Referring to FIGS. 9 and 10 , the entropy decoder 310 of the decodingapparatus may obtain image information from a bitstream. The imageinformation may include prediction related information, residualinformation, information on the HLS, and in-loop filtering relatedinformation. The prediction related information may include inter/intraprediction classification information, intra prediction mode relatedinformation, and inter prediction mode related information. Theinformation on the HLS may include information/syntax for a parameterset being used for decoding of the image/video information. Here, theparameter set may include APS, PPS, SPS, VPS, and the like. The SPSand/or VPS may include PTL information (profile_tier_level syntax) asdescribed above in Table 1 and Table 2. The PTL information may includeprofile information (general_profile_idc) representing a profile towhich output layer sets conform, level information (general_level_idc)representing the level to which the output layer sets conform, tiercontext information (general_tier_flag) for interpretation of the levelinformation, and general constraint information(general_constraint_info) for constraints to which the output layer setsconform.

The entropy decoder 310 of the decoding apparatus may parse, from thePTL information in the bitstream, the level information representing thelevel to which the output layer sets conform, the profile informationrepresenting the profile to which the output layer sets conform, and/orthe tier context information for interpretation of the levelinformation. Further, the entropy decoder 310 of the decoding apparatusmay obtain the general constraint information for the constraints towhich the output layer sets conform from the PTL information in thebitstream (S900). Here, the general constraint information may bepresent next to the level information in the PTL information. That is,the entropy decoder 310 of the decoding apparatus may obtain the generalconstraint information after parsing the level information in the PTLinformation.

The entropy decoder 310 of the decoding apparatus may parse, from thegeneral constraint information, a flag (gci_present_flag) representingwhether the information on the constraints (general constraint flags) ispresent in the general_constraint_info syntax (S910). Further, theentropy decoder 310 of the decoding apparatus may parse the informationon the constraints from the general constraint information based on theflag (S920). For example, if the value of the gci_present_flag is 1, theinformation on the constraints may be included in the general constraintinformation. If the value of the gci_present_flag is 0, the informationon the constraints may not be present in the general constraintinformation.

Meanwhile, the general constraint information may include numberinformation representing the number of bits reserved for the informationon the constraints, the reserved bits, and alignment information(gci_alignment_zero_bit) having the value of 0. The alignmentinformation may be present next to the number information and/or thereserved bits. In other words, the entropy decoder 310 of the decodingapparatus may parse the alignment information after parsing the numberinformation and the reserved bits from the general constraintinformation. For example, the alignment information may be lastly parsedfrom the general constraint information.

The decoding apparatus may perform the decoding procedure for thecurrent picture based on the HLS information including the levelinformation and the general constraint information, the predictionrelated information, and the residual information (S930).

For example, the predictor 330 of the decoding apparatus may generateprediction samples for the current block in the current picture byperforming inter prediction and/or intra prediction for the currentblock in the current picture using the prediction related informationbased on the HLS information obtained from the bitstream. Further, theresidual processor 320 of the decoding apparatus may generate theresidual samples based on the residual information obtained from thebitstream. The adder 340 of the decoding apparatus may generatereconstructed samples based on the prediction samples generated by thepredictor 330 and the residual samples generated by the residualprocessor 320, and may generate a reconstructed picture (reconstructedblock) based on the reconstructed samples.

Thereafter, as needed, in order to enhance the subjective/objectiveimage quality, the in-loop filtering procedure, such as deblockingfiltering, SAO and/or ALF procedure, may be applied to the reconstructedpicture.

Although methods have been described on the basis of a flowchart inwhich steps or blocks are listed in sequence in the above-describedembodiments, the steps of the present document are not limited to acertain order, and a certain step may be performed in a different stepor in a different order or concurrently with respect to that describedabove. Further, it will be understood by those ordinary skilled in theart that the steps of the flowcharts are not exclusive, and another stepmay be included therein or one or more steps in the flowchart may bedeleted without exerting an influence on the scope of the presentdocument.

The aforementioned method according to the present document may be inthe form of software, and the encoding apparatus and/or decodingapparatus according to the present document may be included in a devicefor performing image processing, for example, a TV, a computer, a smartphone, a set-top box, a display device, or the like.

When the embodiments of the present document are implemented bysoftware, the aforementioned method may be implemented by a module(process or function) which performs the aforementioned function. Themodule may be stored in a memory and executed by a processor. The memorymay be installed inside or outside the processor and may be connected tothe processor via various well-known means. The processor may includeApplication-Specific Integrated Circuit (ASIC), other chipsets, alogical circuit, and/or a data processing device. The memory may includea Read-Only Memory (ROM), a Random Access Memory (RAM), a flash memory,a memory card, a storage medium, and/or other storage device. In otherwords, the embodiments according to the present document may beimplemented and executed on a processor, a micro-processor, acontroller, or a chip. For example, functional units illustrated in therespective figures may be implemented and executed on a computer, aprocessor, a microprocessor, a controller, or a chip. In this case,information on implementation (for example, information on instructions)or algorithms may be stored in a digital storage medium.

In addition, the decoding apparatus and the encoding apparatus to whichthe embodiment(s) of the present document is applied may be included ina multimedia broadcasting transceiver, a mobile communication terminal,a home cinema video device, a digital cinema video device, asurveillance camera, a video chat device, and a real time communicationdevice such as video communication, a mobile streaming device, a storagemedium, a camcorder, a video on demand (VoD) service provider, an OverThe Top (OTT) video device, an internet streaming service provider, a 3Dvideo device, a Virtual Reality (VR) device, an Augment Reality (AR)device, an image telephone video device, a vehicle terminal (forexample, a vehicle (including an autonomous vehicle) terminal, anairplane terminal, or a ship terminal), and a medical video device; andmay be used to process an image signal or data. For example, the OTTvideo device may include a game console, a Blu-ray player, anInternet-connected TV, a home theater system, a smartphone, a tablet PC,and a Digital Video Recorder (DVR).

In addition, the processing method to which the embodiment(s) of thepresent document is applied may be produced in the form of a programexecuted by a computer and may be stored in a computer-readablerecording medium. Multimedia data having a data structure according tothe embodiment(s) of the present document may also be stored in thecomputer-readable recording medium. The computer readable recordingmedium includes all kinds of storage devices and distributed storagedevices in which computer readable data is stored. The computer-readablerecording medium may include, for example, a Blu-ray disc (BD), auniversal serial bus (USB), a ROM, a PROM, an EPROM, an EEPROM, a RAM, aCD-ROM, a magnetic tape, a floppy disk, and an optical data storagedevice. The computer-readable recording medium also includes mediaembodied in the form of a carrier wave (for example, transmission overthe Internet). In addition, a bitstream generated by the encoding methodmay be stored in the computer-readable recording medium or transmittedthrough a wired or wireless communication network.

In addition, the embodiment(s) of the present document may be embodiedas a computer program product based on a program code, and the programcode may be executed on a computer according to the embodiment(s) of thepresent document. The program code may be stored on a computer-readablecarrier.

FIG. 11 represents an example of a contents streaming system to whichthe embodiment of the present document may be applied.

Referring to FIG. 11 , the content streaming system to which theembodiments of the present document is applied may generally include anencoding server, a streaming server, a web server, a media storage, auser device, and a multimedia input device.

The encoding server functions to compress to digital data the contentsinput from the multimedia input devices, such as the smart phone, thecamera, the camcorder and the like, to generate a bitstream, and totransmit it to the streaming server. As another example, in a case inwhich the multimedia input device, such as, the smart phone, the camera,the camcorder or the like, directly generates a bitstream, the encodingserver may be omitted.

The bitstream may be generated by an encoding method or a bitstreamgeneration method to which the embodiments of the present document isapplied. And the streaming server may temporarily store the bitstream ina process of transmitting or receiving the bitstream.

The streaming server transmits multimedia data to the user equipment onthe basis of a user's request through the web server, which functions asan instrument that informs a user of what service there is. When theuser requests a service which the user wants, the web server transfersthe request to the streaming server, and the streaming server transmitsmultimedia data to the user. In this regard, the contents streamingsystem may include a separate control server, and in this case, thecontrol server functions to control commands/responses betweenrespective equipment in the content streaming system.

The streaming server may receive contents from the media storage and/orthe encoding server. For example, in a case the contents are receivedfrom the encoding server, the contents may be received in real time. Inthis case, the streaming server may store the bitstream for apredetermined period of time to provide the streaming service smoothly.

For example, the user equipment may include a mobile phone, a smartphone, a laptop computer, a digital broadcasting terminal, a personaldigital assistant (PDA), a portable multimedia player (PMP), anavigation, a slate PC, a tablet PC, an ultrabook, a wearable device(e.g., a watch-type terminal (smart watch), a glass-type terminal (smartglass), a head mounted display (HMD)), a digital TV, a desktop computer,a digital signage or the like.

Each of servers in the contents streaming system may be operated as adistributed server, and in this case, data received by each server maybe processed in distributed manner.

What is claimed is:
 1. A video decoding method performed by a videodecoding apparatus, the method comprising: obtaining general constraintinformation from a bitstream; parsing, from the bitstream, a flagrepresenting whether information on constraints to which output layersets conform is present in the general constraint information; parsingthe information on the constraints from the general constraintinformation based on the flag; and decoding a current picture based onthe information on the constraints, wherein the general constraintinformation includes number information on the constraints and alignmentinformation, and wherein the alignment information is present next tothe number information in the general constraint information.
 2. Thevideo decoding method of claim 1, wherein the flag is present in thegeneral constraint information.
 3. The video decoding method of claim 1,wherein the information on the constraints is not present in the generalconstraint information based on that a value of the flag is
 0. 4. Thevideo decoding method of claim 1, wherein the information on theconstraints and the number information are parsed from the generalconstraint information based on that a value of the flag is
 1. 5. Thevideo decoding method of claim 1, wherein the number informationrepresents the number of reserved bits for the information on theconstraints.
 6. The video decoding method of claim 5, wherein thealignment information is present next to the reserved bits in thegeneral constraint information.
 7. The video decoding method of claim 1,wherein the alignment information is lastly parsed from the generalconstraint information.
 8. The video decoding method of claim 1, whereinthe general constraint information is present in a profile_tier_levelsyntax of the bitstream, wherein the profile_tier_level syntax compriseslevel information representing a level to which the output layer setsconform, and wherein the general constraint information is present nextto the level information in the profile_tier_level syntax structure. 9.A video encoding method performed by a video encoding apparatus, themethod comprising: performing inter prediction or intra prediction for acurrent block in a current picture; generating prediction informationfor the current block based on the inter prediction or the intraprediction; and encoding image information including the predictioninformation, wherein the image information includes a flag representingwhether information on constraints to which output layer sets conform ispresent in general constraint information of the image information,wherein the general constraint information includes number informationon the constraints and alignment information, and wherein the alignmentinformation is present next to the number information in the generalconstraint information.
 10. The video encoding method of claim 9,wherein the flag is present in the general constraint information. 11.The video encoding method of claim 9, wherein the general constraintinformation does not include the information on the constraints based onthat a value of the flag is 0, and includes the information on theconstraints based on that the value of the flag is
 1. 12. The videoencoding method of claim 9, wherein the number information representsthe number of reserved bits for the information on the constraints. 13.The video encoding method of claim 12, wherein the alignment informationis present next to the reserved bits in the general constraintinformation.
 14. The video encoding method of claim 9, wherein thegeneral constraint information is present in a profile_tier_level syntaxof the image information, wherein the profile_tier_level syntaxcomprises level information representing a level to which the outputlayer sets conform, and wherein the general constraint information ispresent next to the level information in the profile_tier_level syntaxstructure.
 15. A non-transitory computer-readable digital storage mediumfor storing a bitstream generated by the image encoding method of claim9.
 16. A method for transmitting data for image information comprising:performing inter prediction or intra prediction for a current block in acurrent picture; generating prediction information for the current blockbased on the inter prediction or the intra prediction; and encoding theimage information including the prediction information, wherein theimage information includes a flag representing whether information onconstraints to which output layer sets conform is present in generalconstraint information of the image information, wherein the generalconstraint information includes number information on the constraintsand alignment information, and wherein the alignment information ispresent next to the number information in the general constraintinformation.